1. Field of the Invention
The present invention is generally related to cooling systems for outboard motors and, more particularly, to a cooling system that provides a closed loop portion for a first set of heat emitting components and an open loop portion for a second set of heat emitting components.
2. Description of the Related Art
Many different types of cooling systems are known, to those skilled in the art, for use in conjunction with outboard motors. Some of these systems are open loop systems, in which water is pumped from a body of water, circulated through various cooling passages of the outboard motor, and then returned to the body of water. Other types of cooling systems for outboard motors utilize a closed loop through which a coolant is circulated in thermal communication with one or more heat emitting components of the outboard motor. In a closed cooling loop system, a heat exchanger is used to remove heat from the coolant.
U.S. Pat. No. 4,260,011, which issued to Brown on Apr. 7, 1981, describes a thermostatically controlled liquid cooling apparatus for outboard motors. The system comprises a closed circuit for circulating a liquid such as fresh water through the portions of an outboard motor to be cooled. The circuit includes a thermostatically controlled mixing valve and a heat exchanger. The mixing valve is disposed between the cooling lines of the outboard motor and the heat exchanger and is connected to an outlet line from the outboard motor, the inlet of the heat exchanger, and an inlet line running from the outlet of the heat exchanger to a cooling line of the outboard motor.
U.S. Pat. No. 5,009,622, which issued to Dudney on Apr. 23, 1991, describes cooling systems for marine motors. The system has a coolant path which is external to the motor housing of the motor. The external coolant path is connected across the inlet and outlet of the internal coolant path through which coolant is normally conveyed to cool the hot zones of the motor. A closed circuit is thus formed. The external coolant path includes a heat exchanger arranged to place the coolant in heat exchange relationship with water in which the motor runs.
U.S. Pat. No. 5,383,803, which issued to Pilgrim on Jan. 24, 1995, describes an outboard motor cooling system. The motor is equipped with a closed circuit cooling system having a coolant pump, a heat exchanger, an expansion tank, a series of coolant passages in the motor and some external piping to complete the circuit. In one embodiment of the invention, a conventional outboard motor is modified to include the closed circuit coolant system with the conventional water pump being converted to the coolant pump.
U.S. Pat. No. 5,921,829, which issued to Iwata on Jul. 13, 1999, describes an outboard motor cooling system. The cooling system includes a first cooling system comprising a coolant path through the engine and an oil cooler for cooling the engine and oil of the lubricating system. The cooling system includes a second cooling system comprising a water path from the body of water in which the motor is operating to a heat exchanger and thereon to a discharge back to the body of water. The first cooling system includes two branches, one branch which passes through the heat exchanger and second branch which does not. A control is provided for routing the coolant through the first branch for cooling within the heat exchanger when the coolant is hot, and for routing through the second branch when the coolant is cool, allowing the engine to warm up.
U.S. Pat. No. 6,513,463, which issued to Katayama on Feb. 4, 2003, describes a cooling system for an outboard motor. It includes a first water passage cooling the engine body and a second water passage branching off from the first water passage upstream of the engine body and extending through the engine components. One engine component is generally positioned above the engine body. Two engine components are positioned on different sides of the engine body. The first and second water passages have separate discharge ports. The engine components are made of a metal material. The second water passage is defined by tubular members made of a corrosion-resistant material and their respective tubular members are embedded in the respective bodies of the engine components.
U.S. Pat. No. 6,544,086, which issued to Tscherne et al. on Apr. 8, 2003, describes a four stroke engine with a cooling system. The cooling system includes a closed loop cooling system for cooling at least a portion of the engine. The cooling system also includes an open loop cooling system for cooling at least a portion of the engine. The open loop cooling system uses coolant from an external source to cool the engine.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
In an outboard motor, certain engine portions and associated components generate heat rapidly upon startup and must be effectively cooled. Other portions of the outboard motor benefit from initially operating at elevated temperatures. Cooling these components immediately after the outboard motor is started may be deleterious for their optimal performance. In addition, cooling all of the components of an outboard motor with a closed cooling system would require a heat exchanger of significant size and weight. Therefore, it would be beneficial if a cooling system for an outboard motor could selectively cool certain preselected components with a closed cooling system and other preselected components with an open cooling system. In order to take full advantage of the closed cooling system, a thermostat controlled bypass can provide additional benefit.